Vehicle fuel systems include evaporative emission control systems designed to reduce the release of fuel vapors to the atmosphere. For example, vaporized hydrocarbons (HCs) from a fuel tank may be stored in a fuel vapor canister packed with an adsorbent which adsorbs and stores the vapors. At a later time, when the engine is in operation, the evaporative emission control system allows the vapors to be purged into the engine intake manifold for use as fuel.
During a refueling event, fuel vapor located in the fuel tank may be diverted to the fuel vapor canister by opening a fuel tank isolation valve prior to the addition of fuel to the fuel tank. Fuel vapors generated during refueling may also be diverted to the fuel vapor canister in this way. Air that is stripped of fuel vapor may be diverted from the fuel vapor canister to atmosphere via a vent line, which may include a vent valve, air filter, etc.
However, restrictions, such as blockages or stuck valves may impede the movement of fuel vapor or air through the evaporative emissions system. In some scenarios, the restrictions may result in the premature termination of a refueling event. As there are numerous potential restriction points within the evaporative emissions system, the cause of premature refueling shutoff is often not apparent. Indeed, the most common solution is a complete dismantling of the evaporative emissions system, which may be time consuming and expensive.
In one example, the fuel vapor canister itself may act as a restriction to the movement of fuel vapor or air through the evaporative emissions system, depending on the loading state of the canister. More specifically, a fully loaded canister may substantially restrict the movement of fuel vapor or air through the canister, as compared to a clean canister. As evaporative emissions standards increasingly become stricter, in some cases it may be necessary to configure a plurality of canisters in series. As such, as the canisters in series become loaded with fuel vapor, the flow of fuel vapor or air through the canister may become increasingly restricted. Accordingly, during a refueling event the increased restriction to fuel vapor flow due to one or more saturated fuel vapor canisters may lead to premature shutoffs. The inventors herein have recognized the above issues.
Toward this end, U.S. Pat. No. 8,191,536 B2 teaches fuel vapor canisters in series, in which the fuel vapors may be supplied to each canister via separate flow paths, thereby providing independent control of the loading of each canister. However, U.S. Pat. No. 8,191,536 B2 teaches during a refueling operation, loading the canisters in series, while during engine-off conditions for which a refueling operation is not indicated, directing the flow of fuel vapors around a first canister to a second canister. As such, the inventors have herein also recognized potential issues with such a method. For example, as described above, during a refueling operation as the canisters become loaded with fuel vapor, the flow of fuel vapor or air through the canisters may become increasingly restricted, leading to premature shutoffs, and U.S. Pat. No. 8,191,536 B2 does not teach actions to mitigate the possibility of increased restriction during refueling operations. Furthermore, U.S. Pat. No. 8,191,536 B2 does not teach directing fuel vapors to separate fuel vapor canisters depending on the loading state of the canisters. Additionally, the directing of fuel vapors to separate fuel vapor canisters as taught by U.S. Pat. No. 8,191,536 B2 is based on the actuation of valves under control of the vehicle powertrain control module, thus increasing costs and complexity of the directing of fuel vapors to separate fuel vapor canisters.
Thus, the inventors herein have developed systems and methods to at least partially address the above issues. In one example, a method is provided comprising, during refueling a fuel tank which supplies fuel to a combustion engine, venting the fuel tank to atmosphere through a vapor storage system (evaporative emissions control system) comprising a first fuel vapor canister and a second fuel vapor canister arranged in series, each comprising a load port and a vent port, and wherein the first fuel vapor canister additionally comprises a purge port; routing vapors from the fuel tank to the load port of the first fuel vapor canister, and responsive to an indication that the first fuel vapor canister is saturated with fuel vapors, routing the vapors from the fuel tank around the first fuel vapor canister to the load port of the second fuel vapor canister.
In one example, a temperature of the first fuel vapor canister may be monitored via a first thermistor positioned at the vent port of the first fuel vapor canister, wherein the indication that the first fuel vapor canister is saturated with fuel vapors includes the temperature of the first fuel vapor canister above a predetermined threshold. Responsive to the temperature of the first fuel vapor canister above the predetermined threshold, a circuit powered by an on-board power supply may be completed based on a temperature dependent change in the resistance of the circuit, wherein completion of the circuit opens a first bypass valve housed within a first bypass conduit running parallel to the first fuel vapor canister such that fuel tank vapors may be routed around the first fuel vapor canister to the second fuel vapor canister. In this way, saturated fuel vapor canisters may be bypassed during a refueling event without powertrain control module input, thus decreasing resistance to the flow of fuel vapor and air through the evaporative emissions system and preventing premature shutoffs of a refueling dispenser due to saturated fuel vapor canisters.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.